I had disc herniation and my mother, who is a retired doctor, said to just do a lot of fast walking. This is the only activity I could do anyways after running marathons just months before. So 10 to 21.1 km walks helped a lot.

I also did some own research. The disks tissue has no blood vessels and the only way to get nutrients is via diffusion, so any activity is essential to accelerate the diffusion and recovery. Walking puts gentle axial load on the spine and knees and is simple and more accessible than e.g. swimming, which is probably even more gentle but hard to do daily for an hour.